I see 2 piece extractors for rim fire mentioned here and like the idea. Has anyone designed one for a center fire, 9 o'clock?  Rimmed case, of course. I made a 9 o'clock, one piece, extractor for a Hauck; a lot of work and iffy results. I do not want to do that again!

gwahir,
I did a sliding extractor in one of my Ballard builds, a 40-70SS much like I do the 22's.  I did hoop stress calculations for it and the safety margin is good (don't recall exact numbers) but I wouldn't want to cut it any closer.  The shank size on my builds is slightly larger than the originals so I had a little more room to work.   I kept the slider width and thickness to a very minimum forcing me to use better materials for it - 17-4ss and heat treated.  Any larger cartridge and I wouldn't even consider it.   
I know there are several early rifles out there that use this design, a rolling block comes to mind and I've looked hard at these and they do cause me to say hmmm with builds I've seen.

I just finished making an extractor for a Hepburn and a Sharps that had slightly different extractor cuts in them, I know the feeling - the one piece is not a favorite of mine either. 
Greg